Seismologists have done preliminary studies on the earthquake and
found that it had some unusual aspects, ones that could help them
better understand earthquakes that happen away from the
boundaries between tectonic plates and better appreciate how
powerful those quakes could potentially be.

Odd earthquake

Unusually, this quake apparently occurred in the middle of an
oceanic plate. All the other top 10 quakes happened at subduction
zones, where one of the tectonic plates making up the Earth's
surface is diving beneath another. [ 13
Crazy Earthquake Facts ]

Also oddly, the Sumatra temblor was a
strike-slip earthquake, where two parts of Earth's crust
slide past each other. Strike-slip quakes are not typically so
powerful — the Sumatra event was "far and away the largest
strike-slip earthquake ever recorded," said researcher Gregory
Beroza, a seismologist at Stanford University. Its magnitude 8.2
aftershock was also among the largest recorded strike-slip
earthquakes.

The reason why this quake was surprisingly powerful might lie in
how deep the faults that triggered it ran, scientists now
suggest.

Seismology readings suggest the Sumatra quake and its aftershock
originated at depths between 25 to 33 miles (40 to 54
kilometers). At those depths, rock is blazingly hot, about 1,110
to 1,470 degrees Fahrenheit (600 to 800 degrees Celsius). At such
temperatures, rock can become viscous at certain points, and in
extreme cases, fault zones may even melt, enabling large amounts
of energy to be released as parts of the Earth slide past each
other.

Mid-plate quakes

Although the Sumatra quake is the only time a temblor in the
middle of an oceanic plate was powerful enough to make the top 10
largest known earthquakes, major earthquakes do regularly occur
in the middle of oceanic plates.

"Oceanic plates cover the majority of the earth, and a lot of
magnitude 8 earthquakes have occurred within the interiors of
oceanic plates in the last few years," said researcher Jeffrey
McGuire, a seismologist at Woods Hole Oceanographic Institution.
"So while the probabilities are extremely low in any one spot,
essentially the majority of the Earth's surface can experience a
magnitude 8 earthquake."

Still, large earthquakes in the middle of ocean plates likely do
not pose much hazard to life or property, since they are well
away from populated areas. They also
usually only generate small tsunamis, although "there is
always a chance that they might set off a submarine landslide —
such landslides have the potential to generate large tsunamis,"
Beroza said.

"The very largest earthquakes that a fault system or plate
boundary is capable of might be larger than was previously
appreciated," Beroza told OurAmazingPlanet. "That's not to say
this is necessarily normal behavior, but it has to be considered
as possible."

Understanding earthquakes that occur within the interior of
oceanic plates is challenging "because we do not have long-term
monitoring networks on the seafloor," McGuiretold
OurAmazingPlanet. "I think one future direction that will be very
interesting is that the National Science Foundation's Cascadia
Initiative is in the midst of a multiyear monitoring effort of
the Juan de Fuca and Gorda plates, which have significant
internal strain. This initiative has the chance to capture a
moderate intra-plate earthquake with nearby instruments which
might really help us understand the processes that lead to the
magnitude 8s that have occurred in more remote locations."

McGuire and Beroza detailed their findings online May 10 in the
journal Science.